I wouldn't recommend an old body on frame car these days. Automotive write Jack Baruth found out the hard way that they don't do so well in crashes, particularly when a side impact is involved:
http://www.thetruthaboutcars.com/2014/01/you-have-questions-i-have-some-answers/
While I don't think a late model Crown Vic would fare as badly as this 1959 Chevrolet did, I still suspect a Fusion or a Taurus would leave the Crown Vic with the worst of the damage:
The Nova was either 189 inches or 196 inches in length. By comparison, a current Malibu is 192 inches, and an Impala is 201 inches. Cars were lower back then and didn't have as much interior volume as a similar length current model.
According to this road test, the 2.8 liter Mustang II's 0-60 time was 14.2 seconds:
http://www.mustangii.net/articles/mustangii_73.asp. By comparison, a current Hyundai Accent will get that done in around 8 seconds. Cars are much faster than they used to be.
I have a daughter who will start driving next year, and I'm going to get her something late model. From an overall safety standpoint, I suspect that a midsize sedan would be best for a teen driver, but I don't think you lose much by going down a size, so she'll probably get something in the Cruze/Civic/Focus/Elantra size range. I want her to have something with all the up to date safety equipment, and the stronger body structure that newer cars have.